Rotary valves of the type described are used, in general, for discharging bulk material from vessels or bins for packaging or transferring them to a conveyor system. Moreover, rotary valves can be used for metering purposes, because, with a predetermined volume of the individual cells, the mass flow can be controlled easily by acting on the revolutions per time unit of the cellular wheel.
Such a rotary valve is supported on either side of the passage for the bulk material within a flange of the housing. The web plates have to be tightened against the inner wall of the housing both in peripheral direction and on the front side. For tightening in peripheral direction, they may be equipped with the sealing strips.
Since most of the bulk materials result in wear of the web plates or the sealing strips, it is advantageous if the web plates are provided with self-adjusting sealing strips radially displaceable within guidances for compensating wear. These sealing strips are biased by pressure which, for example, is generated by deformation of an elastic device, such as a pressure spring. The springs can be accommodated directly within the web plates (EP-A-0 594 949). Since, in this way, at least one pressure spring is needed for each displaceable sealing strip, construction and mounting of the rotary valve are quite expensive. In addition to that, there is a certain susceptibility to trouble, because the springs, and thus the spring forces, are small due to the very narrow space available within the web plates. If a sealing strip jams within its guidance, the spring force is insufficient to overcome the clamping forces so that the peripheral seal will fail.
In another known design (DE 36 23 454), from which the invention initiates, the drive shaft is formed as a hollow shaft. The displaceable sealing strips are biased by radial pressure transmitted from the hollow shaft. To this end, an adjusting device is arranged within the hollow shaft, the device converting the axial force commonly generated by a pressure spring into a radial pressure force by means of two conical actuating surfaces.
This radial pressure force act upon radially displaceable bolts guided within the web plates. The bolts transmit the radial forces onto the displaceable sealing strips of the cell defining web plates.
This construction too is expensive. Due to the cylindrical guidances for the bolts within the cell defining web plates, the latter become necessarily thicker. In this way, the usable cell volume, and thus the mass flow at a predetermined number of revolutions per time unit, are reduced. A further disadvantage of this construction is that the radial forces are transmitted pointwisely onto the sealing strips, leading to high surface pressure in the sliding zones where the components slide on each other and, thus, favoring wear. Furthermore, uniform surface pressure of the sealing strips, as desirable, can only be achieved when using a very hard sealing material which contradicts a good sealing effect. Likewise, unfavorable conditions in transmission of forces exist between the conical actuating surfaces of the adjusting device and the bolts.